For the illumination of motor vehicle instrument panels, especially those using passive elctro-optical display devices large-area illuminants are needed. These large-area illuminants are formed as a light-guide plate into which one or more incandescent lamps can be inserted. Because the available space in a motor vehicle is relatively restricted, it is usual to form the holders for these incandescent lamps in such a way that their overall height including the incandescent lamp is not greater than the thickness of this light-guide plate. Furthermore the problem of heat dissipation is increased in this type of display because incandescent lamps with a relatively high efficiency are needed. Further since some applications require that light must not emerge at the back of the holder, the plate must be constructed to block the emergence of rear lighting.
In general, known illuminating devices which could be used for such applications are formed with contact webs of plastics material fixed on a holder to which the connections to the incandescent lamp are connected. These known embodiments ensure that no light can emerge towards the back, however the heat created by the incandescent lamp can not readily be dissipated. Furthermore it is difficult to secure the contact webs on the insulating holder.